Cinnarizinium 3,5-dinitrosalicylate

The title compound [systematic name: 4-diphenylmethyl-1-(3-phenylprop-2-en-1-yl)-piperazin-1-ium 2-carboxy-4,6-dinitrophenolate], C26H29N2 +·C7H3N2O7 −, is the dinitrosalicylate salt of a tertiary amine. Deprotonation of the carboxylic acid group occurred on the phenolic hydroxy group. The diazacyclohexane ring adopts a chair conformation. Intramolecular O—H⋯O and intermolecular C—H⋯O and N—H⋯O hydrogen bonds are observed. The N—H⋯O hydrogen bonds are bifurcated at the H atom and connect the cinnarizinium and 3,5-dinitrosalicylate ions together. Intermolecular C—H⋯O hydrogen bonds connect the components into layers perpendicular to the crystallographic a axis.


Comment
Cinnarizine is an antihistamine which is mainly used for the control of nausea and vomiting due to motion sickness. A clinical evaluation of cinnarizine in various allergic disorders is published (Barrett & Zolov, 1960). The crystal structures of some related compounds such as cyclizine hydrochloride (Bertolasi et al., 1980), guanidinium 3,5-dinitrosalicylate (Smith et al., 2001) and cinnarizine dipicrate (Jasinski et al., 2011) have been reported.
Deprotonation occurred at the phenolic hydroxy group while the carboxyl group remains in its protonated state.
Protonation occurred on the nitrogen atom bearing the vinylic substituent. The 1,4-diazacyclohexane moiety adopts a 4 C 1 ( N2 C N1 ) conformation (Cremer & Pople, 1975). The least-squares planes defined by the carbon atoms of the aromatic moieties on the diphenylmethyl substituent enclose an angle of 66.06 (8)° and intersect with the plane defined by the phenyl group bonded to the vinylic substituent at angles of 16.76 (9)° and 72.01 (9)°, respectively. The least-squares planes defined by the individual phenyl groups of the cation enclose angles of 37.54 (9)°, 53.70 (8)° and 79.26 (8)° with the corresponding plane of the carboxylic acid ( Fig. 1).
In the crystal, intramolecular O-H···O and intermolecular C-H···O and N-H···O hydrogen bonds in are observed.
The N-H···O hydrogen bonds are bifurcated at H7. A graphical representation in terms of donor and acceptor atoms for a selection of these contacts is given in Figure 2. In terms of graph-set analysis, (Etter et al., 1990;Bernstein et al., 1995), the descriptor for the hydrogen bonds is S(6)DD on the unary level while the C-H···O contacts necessitate a DD descriptor on the same level. The C-H···O hydrogen bonds connect the components together into layers perpendicular to the crystallographic a axis (Fig. 2). The shortest intercentroid distance between two aromatic systems was measured at 4.2848 (11) Å and is apparent between the phenyl group conjugated to the vinylic system and the aromatic ring of the dinitrosalicylate anion.

Experimental
Cinnarizine (3.68 g, 0.01 mol) and 3,5-dinitrosalicylic acid (2.28 g, 0.01 mol) were dissolved in hot acetone and stirred over a heating magnetic stirrer for few minutes (330 K). The resulting solution was allowed to cool slowly at room temperature. The salt formed was filtered and dried in a vaccum desiccator over phosphorous pentoxide. The compound was recrystallized from a mixture of DMSO and acetonitrile (v:v = 1:1) by slow evaporation (m.p.: 383 K).

Refinement
Carbon-bound H atoms were placed in calculated positions (C-H 0.95 Å for vinylic and aromatic C atoms, C-H 0.99 Å) and were included in the refinement in the riding model approximation, with U(H) set to 1.2U eq (C). The nitrogenbound H atom was located on a difference Fourier map and their coordinates as well as isotropic displacement parameters were refined freely.